<p>Material systems that exhibit tunable spin-selective conductivity are key components of spintronic technologies. Here, we demonstrate a mechanism for spin-selective transport that is based on the unusual Landau-level sequence observed in bilayer WSe₂ under large applied magnetic fields. We find that the conductivity depends strongly on the relative ordering between conducting electrons with different spins and valleys in a partially filled Landau level and the localized electrons of lower-energy filled Landau levels. We observe that the conductivity is almost completely suppressed when the spin ratio and field-tuned Coulomb energy exceed a critical threshold. We achieve switching between on and off states through either modulation of the external magnetic or electric fields, with many-body interactions driving a collective switching mechanism. In contrast to magnetoresistive heterostructures, this mechanism achieves electrically tunable spin filtering within a single material, driven by the interaction between free and localized spins residing in energy-separated spin-and-valley-polarized bands. Similar spin-selective conductivity may be realizable in flat-band systems at zero magnetic field.</p>